The present invention relates to a sliding bearing device for continuous molten metal plating bath rolls.
Continuous molten metal plating of metal band is generally operated in a process as shown in FIG. 3. A metal strip, for example, a steel strip 1 is guided into a plating cell 3 from a annealing furnace not shown through a snout 2, and is inverted in an upward direction by bath sink rolls 4, and is straightened by bath support rolls 5, and leaves the plating cell. By wiping nozzles 6, further, the deposit amount of plating metal such as zinc is adjusted to a specified value. To make the deposit amount uniform, it is important to stabilize the pass line of the metal strip 1 at the wiping point, and the pass line is stabilized by the bath support rolls 5 and upper support rolls 7. The metal strip 1 is then sent into an alloying furnace 8 of a next step.
Bearings used in the sink rolls 4 and bath support rolls 5 are sliding bearings of bush structure in most cases, and the bearing material is metal such as stainless steel or the like, metal+WC sprayed layer, carbon, and others, and gradual wear during operation causes various problems, such as variation of pass line, vibration of roll and shortening of roll replacement interval. Besides, since the worn bearing cannot be used again, the repair cost becomes high.
To solve these problems, hitherto, various techniques have been proposed: for example, as disclosed in Japanese Patent Application Laid-open No. 10-317119, a glass ceramic layer is disposed on the surface of the bearing, and a groove is formed in the thrust surface of the bush side to lower the abrasion coefficient of the bearing, or as disclosed in Japanese Patent Application Laid-open No. 11-256300, a partial cylindrical hard ceramic sinter is used as the bearing material, and a boron nitride application layer is disposed between it and a steel retainer so as to be used for a long period. Besides, Japanese Patent Application Laid-open No. 4-124254, Japanese Patent Application Laid-open No. 5-44002, Japanese Laid-open Utility Model No. 5-69155, and Japanese Patent Application Laid-open No. 6-306560 disclose a bearing structure of fitting metal retainer and ceramic directly, and in particular Japanese Patent Application Laid-open No. 6-306560 proposes a semi-cylindrical or partial cylindrical ceramic, in which the angle of two straight lines linking the center of rotation of the shaft and both ends in the peripheral direction of the inside of the ceramic is 20 to 90 degrees.
These prior arts, however, have the following problems.
(1) When the temperature is changed several times by lifting and dipping the rolls repeatedly, in the case of ceramic bearing material, in a structure of steel retainer filled with cylindrical ceramic, the difference of thermal expansion between steel and ceramic is large, and a compressive force is applied to the ceramic by the residual zinc between the steel retainer and the cylindrical ceramic in the shrinking process, and finally the cylindrical ceramic is broken.
(2) In the bearing structure disclosed in Japanese Patent Application Laid-open No. 10-317119, the glass ceramic layer may be peeled by thermal stress, and the glass ceramic layer must be coated again, thereby increasing the repair cost.
(3) In the bearing structure disclosed in Japanese Patent Application Laid-open No. 11-256300, it takes much time and labor in maintenance, and moreover if zinc invades into the gap, its compressive force may lead to fracture.
(4) In the bearing structure disclosed in Japanese Patent Application Laid-open No. 4-124254, Japanese Patent Application Laid-open No. 5-44002, or Japanese Laid-open Utility Model No. 5-69155, zinc invades into the gap, or the ceramic may be broken by thermal stress, and countermeasures are not sufficient.
(5) In the bearing structure disclosed in Japanese Patent Application Laid-open No. 6-306560, breakage of ceramic can be prevented, but the shaft is likely to separate from the ceramic during operation, and vibration of steel band or uneven wear or the like of shaft may occur, and stable operation may not be realized.
It is hence an object of the invention to solve the problems of these prior arts, and provide a sliding bearing device for continuous molten metal plating bath rolls excellent in durability, and contributing to stable operation of continuous molten metal plating.
The solve the problems, the invention presents a sliding bearing device for continuous molten metal plating bath rolls, in which a shaft and a bearing composed of a hard ceramic sinter sliding and contacting with said shaft are retained displaceably by a steel retainer.
In the invention, the bearing rolls with its back side in contact with the inside of the retainer, and its inside is desired to be displaceable by rolling in contact with the roll shaft.
Also, according to the invention, the bearing preferably forms a partial cylindrical shape with an effective angle from over 90 degrees to 160 degrees. Preferably, the effective angle is 100 degrees to 160 degrees.
In the invention, preferably, the inside of the retainer and the back side of the bearing contact with each other by setting the radius of curvature of the former large than that of the latter. Specifically, the ratio of the radius of curvature of the inside of the retainer and the back side of the bearing is from over 1.0 to 1.5. Preferably, the ratio of the radius of curvature is from over 1.0 to 1.2.